i noticed most of the k-dramas have this trend in their romance series - sleeping on the other person's shoulder. especially during long bus or train rides.
here's a few that i can recall:
1) 겨울연가 / Winter Sonata
actually this scene is after Joon Sang pushed Yoo Jin's head off his shoulder. tskkk.
2) 풀하우스 / Full House
3) 꽃보다 남자 / Boys Over Flowers
4) 우리 결혼했어요 / We Got Married - CN Blue Yong Hwa & SNSD Seo Hyun
5) 넌 내게 반했어 / Heartstring
6) 시티헌터 / City Hunter
7) 신의 / Faith
and still keeping the trend, 8) 상속자들 / The Heirs
so, trend#1 - sleep on shoulder - checked!
no wonder abz's shoulder is my favorite place to sleep :)